Re: [dpdk-dev] [PATCH] net/i40e: fix mbuf fast free wrong check

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Yang, MurphyX <murphyx.yang@intel.com>
> Sent: Wednesday, April 7, 2021 2:37 PM
> To: dev@dpdk.org
> Cc: Yang, Qiming <qiming.yang@intel.com>; Guo, Jia <jia.guo@intel.com>;
> Xing, Beilei <beilei.xing@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>; Yang,
> SteveX <stevex.yang@intel.com>; Zhang, RobinX <robinx.zhang@intel.com>;
> Yang, MurphyX <murphyx.yang@intel.com>
> Subject: [PATCH] net/i40e: fix mbuf fast free wrong check
> 
> If no offload flags are set, then 0 == 0 & <anything> is true.
> This means that if DEV_TX_OFFLOAD_MBUF_FAST_FREE is not set (and no
> other flags are set) then this check will still enable `tx_simple_allowed`.
> 
> This patch adds the 'offloads' flag not equal zero to avoid this scenario.
> 
> Bugzilla ID: 665
> Fixes: 399421100e08 ("net/i40e: fix missing mbuf fast free offload")
> 
> Signed-off-by: Murphy Yang <murphyx.yang@intel.com>
> ---
>  drivers/net/i40e/i40e_rxtx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c index
> b3d7765e3b..1450b228ca 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -3345,7 +3345,7 @@ i40e_set_tx_function_flag(struct rte_eth_dev *dev,
> struct i40e_tx_queue *txq)
> 
>  	/* Use a simple Tx queue if possible (only fast free is allowed) */
>  	ad->tx_simple_allowed =
> -		(txq->offloads ==
> +		(txq->offloads != 0 && txq->offloads ==
>  		 (txq->offloads & DEV_TX_OFFLOAD_MBUF_FAST_FREE) &&

I don't think this is correct.

Why simple_tx can't be selected if no DEV_TX_OFFLOAD_MBUF_FAST_FREE is required?

Actually, the original code means, the max Tx offload that simple_tx support is DEV_TX_OFFLOAD_MBUF_FAST_FREE, you can't have more than it, but cannot have it.


>  		 txq->tx_rs_thresh >= RTE_PMD_I40E_TX_MAX_BURST);
>  	ad->tx_vec_allowed = (ad->tx_simple_allowed &&
> --
> 2.17.1